The present invention is particularly useful in the fields of hematology, flow cytometry and blood chemistry in which it is often necessary to dispense relatively small volumes (e.g. 1-30 microliters) of whole blood and/or a prepared blood sample with high precision and in an automated way. The invention, however, can also be used when assaying other body fluids, as well as in the field of analytical chemistry in which similar requisites might be fulfilled.
In conducting tests on samples of biological liquids, it is common to provide the sample to an automated analyzer in test tubes or vials that are either open or sealed, typically by a rubber stopper, and arranged on a sampling tray close to each other. Upon receiving the sampling tray with a multiplicity of vials containing samples, the vials are transported, one after the other, to a sampling station formed preferably in the analyzer itself where the tip of the sampling member enters the sample volume. Depending on the situation whether the vial is open or sealed, i.e. closed, said tip can be a sharpened portion of the sampling member or it is provided simply by just a butt end thereof. To help with collecting biological liquids of interest, particularly whole blood, from humans or animals, closed vials are manufactured with a certain amount of vacuum inside that may partially remain within the vial after completion of collection. This implies that the value of pressure in the vial is unknown at the time of collecting the sample.
To perform a measurement on the vial, at first a portion of the sample in said vial is taken out, i.e. aspirated from the vial into the tip of the sampling member. Then at least a tiny aliquot of the aspirated sample is dispensed into a mix chamber where in most cases it gets prepared for the analysis, i.e. appropriately diluted before being analyzed. Special care should be devoted to the sampling of open vials, as these should be kept in a vertical position over the whole sampling procedure in order to avoid spilling of the sample contained in the vial.
Hematology analyzers, in general, are intended for performing a complete blood count and hemoglobin measurement in human or animal whole blood. To actually perform the measurement, a hematology analyzer prepares a mix solution, with high precision, from the aliquot amount of blood sample aspirated from the vial by diluting it to about 250 times in the mix chamber using an isotonic diluent. To achieve high precision, the amount of blood used in the dilution should be very accurate as well.
In general, the liquid aspirating and dispensing means of automated hematology analyzers is one of two types: (i) those that basically use a precision syringe pump connected to the sampling member for both sucking a portion of the blood sample from its vial and then dispensing a metered aliquot amount thereof through the same sampling member into the mix chamber (this is often referred to as the “suck-and-spit” technique), and (ii) those that aspirate said blood sample into a blood sampling valve (“BSV”), or shear valve assembly, that segments the aspirated sample into one or more precise aliquots for subsequent dispensing by means of exploiting a so-called aliquoting chamber formed as integral part of the blood sampling valve. Both sampling techniques have some advantages and disadvantages, just to mention in case (i) the problem of accuracy regarding the aspiration and/or dispensing that depends, actually, on the accuracy of moving the plunger of the syringe pump in opposite directions, and in case (ii) the problems of considerable manufacturing costs and relatively large volumes of spoiled sample, as discussed in U.S. Pat. No. 7,661,326 B2 (Li et al.) in detail. To eliminate or at least alleviate disadvantages of the above-discussed techniques, U.S. Pat. No. 7,661,326 B2 discloses a kind of ‘hybrid’ technique, according to which the high accuracy in aliquoting provided by the BSV technique is combined with the lower volume sample consumption of the suck-and-spit technique.
In particular, U.S. Pat. No. 7,661,326 B2 teaches a hybrid sampling apparatus to be used in an automated analytical instrument, comprising a sampling member to effect sampling, a transport system for selectively advancing said sampling member to take (or dispense) liquid sample from (or to) different containers spaced apart, a sampling valve assembly operatively connected to the sampling member to perform aliquoting and dispensing, and a pump operatively connected to the sampling valve assembly and selectably operable to either (i) draw a liquid sample through the sampling member and through the valve assembly to fill at least one aliquoting chamber thereof, or (ii) to dispense the aspirated liquid sample through the sampling member into one or more mix chambers. After being taken out, the sample is moved by the pump along a sample flow path that includes the passageway of the sampling member in its full length, as well as a complicated arrangement of interconnected bore holes and surface grooves formed in or on the surfaces of valve pads constituting the shear valve assembly. Due to the construction, the sample travels a relatively long way within the hybrid sampling apparatus from the sample container(s) to the mix chamber(s). Or putting this another way, the hybrid sampling apparatus suffers from the disadvantage of long sample flow path.
Due to physical/chemical properties and composition of body fluids as the sample, in particular whole blood, a portion of the sample transferred from a sample container to a mix chamber tends to adhere on the internal wall of the flow path, i.e. the tubing used for the transfer. This increases sample demand when sample is taken out. Moreover, as is found experimentally, various components of body fluids have different tendencies for adhering on the tubing wall. Adhering might cause, in turn, a qualitative distortion in the composition of the sample to be studied and thus the final measuring data. The longer, hence, the flow path said sample has to run within the sampling device, the higher is the probability of said qualitative distortion. In light of this, it would be advantageous to decrease, in particular, minimize the length of the flow path to be travelled along by the sample within a sampling apparatus.
A possible way to decrease the sample flow path is to integrate the sampling member directly into the sampling valve; such a solution is known in the prior art in the form of a BSV with a sampling member fixed into it in the upward pointing position. Hence, to perform sampling with the device, the sample tube has to be turned upside-down. As is clear, this kind of a sampling device is not applicable with open sample tubes. A yet further disadvantage of the device arises when its application in automated analyzers comes about: in such cases, the analyzer should be equipped with a suitable turning mechanism to turn the individual sample tubes into the upside-down position for sampling and then back for storage which would clearly retard the sampling procedure and increase the costs of both sampling and manufacturing.
U.S. Pat. Nos. 4,463,615 and 4,507,977 equally teach liquid metering and transfer valves wherein a sampling member is integrated into the metering valves.
U.S. Pat. No. 6,662,826 B1, regarded as the closest prior art, discloses a multi-disc liquid metering and transfer valve with a port switch valve disc having at least two inlet connections, i.e. a sampling unit to dispense a given volume of liquid sample in accordance with the preamble of claim 1. Said metering and transfer valve is provided with a relatively long sampling path. Thus, in operation, the adherence of sample on the walls of the sampling path is increased that greatly influence the quality of the sample dispensed. Furthermore, to dispense the given volume of liquid sample, said metering and transfer valve performs lateral movements which require additional space during operation.
Precision of sampling is of high interest in the case of analytical instruments, such as e.g. a HPLC equipment or various body fluid analyzers, like the automated hematology analyzers. In certain cases, only tiny amounts of sample are available. The smaller the sample volume to be worked with is, the more difficult it is to achieve the high precision when dispensing is performed. If the dispensed sample should be diluted before its further processing, the amount of diluent also matters; to achieve a certain preset concentration required by a measurement or testing, it is obvious that smaller sample volumes require less diluent.
Hence, to save costs, it is a continuous task in analytics to decrease the volume of the sample to be assayed and also to use it up efficiently (i.e. essentially completely, possibly without flushing a portion thereof to waste), along with—if possible—increasing, but at least maintaining the level of precision when said volume is dispensed.